This invention relates to a hardenable coating composition which comprises, as the principal component, an aqueous dispersion of silica-polyvinyl alcohol complex. More particularly, the invention relates to a hardenable coating composition which forms an excellent coating film having desirable properties such as transparency, water resistance, mechanical properties, flexibility and noncombustibility. Further, this invention relates to a hardenable coating composition of silica-polyvinyl alcohol complex dispersion which contains alkoxy silanes as a reaction accelerator. Furthermore, this invention relates to a hardenable coating composition of silica-polyvinyl alcohol complex dispersion in which the properties of coating film to be formed can be improved by the addition of curing agents such as alkoxides, complexes, water soluble metallic salts and coordination compounds.
In order to produce a novel industrial material to form coating film having the good adhesion, covering property and flexibility characteristic of organic polymers and hardness and the noncombustibility characteristic of inorganic materials, the present inventors have carried out eager and extensive studies on a wide variety of raw material. As the result of experiments, the inventors have discovered that silica (silicon dioxide or silicic acid anhydride) combines easily with organic polymers containing hydroxy groups, especially with polyvinyl alcohols under specific reaction conditions to form silica-polyvinyl alcohol complex. Further, it has been also found that this silica-polyvinyl alcohol complex meets the above-mentioned requirements. Furthermore, in accordance with the additional experiments, it has been found that the reaction to form the silica-polyvinyl alcohol complex can be promoted by the addition of a certain compound, and the curing and film properties of obtained film can be much improved by the addition of curing agents to the coating composition.
Thereby the present invention on the hardenable coating composition has been accomplished.